Search tab (#5754)

* Add a developer flag for the search tab
Introduces a globalSearchEnabled user preference (off by default) with a toggle in Developer Options, used to gate the new search experience.

* Support search role tabs in the tab coordinator
Migrates the NavigationTabCoordinator to SwiftUI's value-based Tab API and adds an isSearch option so a tab can adopt the iOS 26 .search role, which detaches it into the trailing search button in the tab bar.

* Moves room search to a new screen
Adds a new screen that filters the alternate room summary provider as you type, shows an empty state, and lists matching rooms with their matrix identifier. Supports hardware keyboard selection (arrow keys to move through results, return to open) by reaching into the system search field.

* Present search in a dedicated tab
Adds the search tab to the chats flow on iOS 26 when the flag is enabled, rendered as the detached .search role button. The Cmd+K shortcut now selects this tab, and the home screen's inline search is hidden while the tab is available.

* Remove the old global search screen
The dedicated search tab replaces the Cmd+K floating window, so the GlobalSearchScreen, its window plumbing in the WindowManager, and its presentation in the chats flow are all removed.

ElementX/Sources/Application/Navigation/AppRoutes.swift

@@ -54,8 +54,8 @@ enum AppRoute: Hashable {
     case transferOwnership(roomID: String)
     /// A thread within a room, only to be used to handle tap on notification for threaded events.
     case thread(roomID: String, threadRootEventID: String, focusEventID: String?)
-    /// The global search screen
-    case globalSearch
+    /// The search screen
+    case search
     
     /// Whether or not the route should be handled by the authentication flow.
     var isAuthenticationRoute: Bool {

ElementX/Sources/Application/Navigation/NavigationTabCoordinator.swift

@@ -23,17 +23,21 @@ import SwiftUI
         let title: String
         let icon: KeyPath<CompoundIcons, Image>
         let selectedIcon: KeyPath<CompoundIcons, Image>
+        /// When `true` the tab is given the `.search` role, which on iOS 26 detaches it
+        /// into the trailing search button in the tab bar.
+        let isSearch: Bool
         var badgeCount = 0
         
         /// Provide the tab's split coordinator in here to have the tab bar automatically hidden
         /// when pushing a child into the split view's details on iPhone/compact iPad.
         weak var navigationSplitCoordinator: NavigationSplitCoordinator?
         
-        init(tag: Tag, title: String, icon: KeyPath<CompoundIcons, Image>, selectedIcon: KeyPath<CompoundIcons, Image>) {
+        init(tag: Tag, title: String, icon: KeyPath<CompoundIcons, Image>, selectedIcon: KeyPath<CompoundIcons, Image>, isSearch: Bool = false) {
             self.tag = tag
             self.title = title
             self.icon = icon
             self.selectedIcon = selectedIcon
+            self.isSearch = isSearch
         }
         
         func barVisibility(in horizontalSizeClass: UserInterfaceSizeClass?) -> Visibility {
@@ -294,18 +298,18 @@ private struct NavigationTabCoordinatorView<Tag: Hashable>: View {
     var body: some View {
         TabView(selection: $navigationTabCoordinator.selectedTab) {
             ForEach(navigationTabCoordinator.tabModules) { module in
-                module.coordinator?.toPresentable()
-                    .id(module.id)
-                    .tabItem {
-                        Label {
-                            Text(module.details.title)
-                        } icon: {
-                            CompoundIcon(module.details.tag == navigationTabCoordinator.selectedTab ? module.details.selectedIcon : module.details.icon)
-                        }
+                Tab(value: module.details.tag, role: module.details.isSearch ? .search : nil) {
+                    module.coordinator?.toPresentable()
+                        .id(module.id)
+                        .toolbar(module.details.barVisibility(in: horizontalSizeClass), for: .tabBar)
+                } label: {
+                    Label {
+                        Text(module.details.title)
+                    } icon: {
+                        CompoundIcon(module.details.tag == navigationTabCoordinator.selectedTab ? module.details.selectedIcon : module.details.icon)
                     }
-                    .tag(module.details.tag)
-                    .badge(module.details.badgeCount)
-                    .toolbar(module.details.barVisibility(in: horizontalSizeClass), for: .tabBar)
+                }
+                .badge(module.details.badgeCount)
             }
         }
         .backportTabBarMinimizeBehaviorOnScrollDown()